Moving partitions is done like John wrote, you can enqueue moving p8 … p4 and apply everything at once.
~300 GiB > ~150 GiB, so more copying (entire partition are being copied, bit by bit), less clicking to copy one partition, but moving few smaller ones is faster anyway.
Booting from n1p3 will fail after removing it (copied partition will have a different ID and no longer be the n1p3, but n1p9 instead), automatic windows repair should fix it, but it’ll have to be run first.
Expanding bitlocker encrypted partition from within windows is at least a precaution, I don’t know about it’s support in GParted, I’d use windows disk manager anyway, it’s just safer that way.
Exactly.